Microsoft says 64 GB is the 'ideal spec' for Flight Simulator 2024 but I've tested it with 96 GB, and it makes a big difference
Update: Further testing has shown that while Flight Simulator 2024 is running, the total system RAM usage doesn't exceed 30 GB, regardless of the amount installed. So the use of 96 GB doesn't fully explain the performance gains over 64 GB; however, the frame rates were checked again and found to be the same.